The main components of a drive train of a motor vehicle are an engine and a transmission. A transmission converts torque and rotational speeds into the driving force of the engine. The present invention relates to a method for operating a drive train that comprises at least an automatic transmission and a hybrid drive for the power plant.
US 2005/0221947 A1 discloses a method for operating a motor vehicle drive train comprising at least an automatic transmission and a hybrid drive, where at one side a clutch is arranged between a combustion engine of the hybrid dive and an electric motor of the hybrid drive, while at the other side another clutch is arranged between the electric motor of the hybrid drive and the automatic transmission. When the drive train is driven exclusively by the electric motor of the hybrid drive, the internal combustion engine of the hybrid drive can be started, according to the prior art, by engaging the clutch arranged between the internal combustion engine and electric motor of the hybrid drive, while the automatic transmission of the drive train is upshifting. According to US 2005/0221947 A1, the electric motor of the hybrid drive starts the internal combustion engine of the hybrid drive, causing a change in rotational speed at the transmission output of the automatic transmission, which the driver usually perceives as a disturbance.